Accurate electrophysiological neuroimaging using high density EEG and MEG increasingly requires knowledge of both head geometry and electrical conductivity. Head and brain geometry can be obtained from structural tomographic techniques such as CT and MRI, but the conductivity of different head tissues cannot currently be measured. We propose to demonstrate the feasibility of a technique for measuring human scalp, skull, and brain conductivities noninvasively using low-level scalp current injection. The process will first be modeled with computer simulations including the effect of noise and measurement errors. Prototype hardware will be constructed to provide the necessary switching and current injection circuitry, then tested with physical models having known geometry and conductivities. Finally, the entire system will be applied to human subjects to demonstrate its overall practicality. With accurate conductivities, realistic head-brain models can be constructed for individual subjects or patients, making EEG/MEG inverse procedures for spatiotemporal localization of neurological activity more accurate as well. In addition, since the conductivity estimation procedure will only take a few minutes, changes in conductivity can be tracked over time scales appropriate for following abnormal physiological changes associated with stroke, epilepsy, and head injury. PROPOSED COMMERCIAL APPLICATION: The head conductivity scanner will be a useful and necessary addition to any research or clinical EEG/MEG lab that utilizes quantitative inverse methods, alone or in conjunction with other functional imaging modalities such as PET,SPECT, or fMRI.